The seedling stage is different for photo plants than it is for autos. For autos you should plant the germinated seed directly into the final pot and avoid transplanting. For photo plants if you followed the germination directions in the previous post you now have a sprout in a solo cup.
As the plant grows the cotyledon leaves will eventually die off. Nothing to worry about there, even if the first single true leaves show signs that something may be wrong. I consider this the plant’s growing pains as it gets settled into its growing medium. It may look yellow like it needs feeding, or twisted like the PH is off, but this is normal and the plant will grow out of it.
This solo cup stage is where you start learning the skill of feeling the weight difference of wet soil and dry soil. If you put your holes in the bottom of the solo cup you will have proper drainage. You will be able to water the soil as needed and any run off will run out of the bottom of the cup. Make sure you let enough run out of the cup so that when you put it back into the other cup without holes it won’t fill that one up more than a few drops. Let the soil dry almost all the way between watering.
You will do this from anywhere from a week to 4 weeks. That is up to you and the plant. You will have to judge the plant on when it is ready to transplant. A wise old man once told me that if the leaves reach the edge of the cup then it is ready. While I think that that may be a little early, its ok to follow the rule.
Signs that it is time to transplant to a larger pot are roots growing out of the bottom of the cup or a sad droopy look to the seedling no matter if its been watered or in dry soil. Usually the seedling won’t be much taller than a solo cup at this point.
Some people prefer to transplant several times moving up in sizes. I personally like to transplant just once. My plants go from a solo cup right into a 7 gallon fabric pot. This is the opportunity to cover the trunk all the way up to where the cotyledons were. After transplant the seedling may be a little shocked and might slow down growth for a few days. Don’t worry, that’s normal. It may even look wilted and sad but trust that it will bounce back.
Now that your seedling has been transplanted, it is time to think about the vegetative stage and training. This is where the real fun begins.